Contrast media are substances used to enhance the contrast of structures or fluid within the body in the medical imaging field. Among the imaging techniques currently employed, the magnetic resonance imaging (MRI) is one of the most relevant, due to its efficacy and safety and, in this prospect, several contrast media have been developed during the last decades. Said MRI contrast media comprise, basically, a paramagnetic metal (generally gadolinium) which is complexed with a poliammino carboxylic chelate, either cyclic or acyclic. Examples of said paramagnetic complexes are Gd-DTPA, Gd(HP-DO3A) and Gd-BOPTA. In particular, the physiologically compatible salt of this latter (i.e. the dimeglumine salt see The Merck Index, XII Ed., 2001, Nr 4344), referred also as gadobenate dimeglumine complex, of Formula I below, represents the active ingredient of one of the most commonly used MRI contrast agent, commercially known as MultiHance®.

MultiHance® is obtained for instance as disclosed in EP0230893.
It has to be noted that the degree of purity is for contrast agents, as well as for pharmaceutical compounds in general, of a critical issue. In particular for pharmaceutical compounds to be injected, quality standards are in fact very restricting to fully satisfy all the competent authorities requirements.
In the imaging field, accordingly, the contrast: agent has to be prepared in a pure, stable and convenient physical form and, in the most of the cases, this represents a crucial point and a challenge that any manufacturer has to face. A suitable physical form should be, for instance, the one that allows, first of all, a reliable and practical recovering of the compound in the final form ready to be administered, such to guarantee a safe and prolonged storage of the product.
In this respect, and whenever possible, the solid form of a chemical compound is generally preferred. In fact, when the product is obtained in a liquid or oily form or in a solution or suspension thereof, several isolation and purification techniques are further employed to convert such a product into the corresponding solid form (see for instance, Huang et al., Advanced Drug Delivery Reviews; 2004; 56; 321-334).
Among known processes, the selective precipitation from a proper solution, the evaporation of the solvent, the lyophilisation and the crystallization from a suitable organic solvent, or from a mixture of solvents, are some examples of methodologies widely used to this extent (see for example: TUMJ; 2001, 59(3), 53-59 and Palermo et al. Chemical Reviews; 1968; Vol. 60; 65-93).
The cited procedures, taken alone or even in any combination thereof, are currently employed, from the bench to the industrial scale, when a final solid form of a chemical compound is desirable or required, for example for workability reasons or for the preparation of a convenient solid drug dosage form. Typically, a filtration and a final drying step, usually under reduced pressure, are carried out in order to collect the product of choice as a dried solid (see for a general reference, Takashi et al. Journal of the Society of Powdered Technology, 2006; Vol. 43; No 12; 882-889).
Spray-drying technique represents an alternative method to the above, where a solid compound is collected starting from a proper solution (usually, an aqueous solution or a suspension of the same, by a spray-dryer device. This technique, however, suffers from some drawbacks, in particular when applied to molecules with specific chemical features, such as for instance, organic complexes or the like. In fact, some structural and/or chemical physical changes may be observed, including, among others, polymorphic changes, solvate formation or even undesirable glassy forms of the product (for a general reference, see for example, Corrigan et al., Thermochimica Acta 248; 1995; 245-258).
We have now surprisingly found that when a proper liquid composition of the gadobenate dimeglumine complex is subjected to a spray-drying procedure, the solid form thus obtained may be conveniently collected in high and reproducible yields and, noteworthy, said solid form substantially maintains the specifications of the starting liquid composition, even when the latter is intended for the administration and therefore in conformity with the limits and the specifications required for safety reasons.